In a drilling operation a drill bit is mounted to the end of a drill string. The drill string is rotated from the top of the string or by a motor at the bottom of the string, or both, to rotate the drill bit and advance the borehole. Universal joints are included in the drill string to accommodate eccentricity in the string. The eccentric rotation must be converted into concentric rotation in order for the drill bit to advance the borehole efficiently. Eccentricity in the drill string may be initiated by a motor in the drive assembly that rotates the drill bit or by steering of the bit to change direction of the borehole.
The components of the drill string including the universal joint are subjected to extreme torque forces, elevated operating temperatures and abrasive drilling fluids, all of which can have an adverse effect on the operational life of drill string components. The constant relative movement of the components of the universal joint, together with abrasive drilling mud, causes abrasion and erosion of mating components. Attempts have been made to effectively seal the universal joint assemblies so as to prolong their operational life. Due to the constant relative movement of the components of the universal joint, they do not readily lend themselves to conventional sealing arrangements. Universal joint wear results in pitting of the bearing surfaces from the abrasive drilling fluids. Replacement of the joint or its components requires removal of the drill string from the borehole and downtime for the operation which increases operational expenses substantially.
A universal joint that is less vulnerable to abrasion and erosion with an extended service life would be advantageous.